In this application area, the use of mechanical connections for connecting reinforcement bars, in order to ensure the transmission of mechanical stresses in a continuous manner, is known. These reinforcement bars have nervures or ribs on their external surface. The nervures or rubs have dimensions which are rather irregular but are of course proportioned relative to the diameter of the bar.
Presently, it is known to connect these bars by spot-connecting using a tube jointing sleeve which is crimped over by pressing. For this it is necessary to use awkward shaped exterior clamping jaws since the system which uses a clamping jaw that wraps by external pressure must be powerful. This obstruction is a disadvantage when the concentration of reinforcement bars is increased because if two reinforcement bars are very close together, it is not possible to act rapidly on the construction site.
It is also to be noted that after the clamping jaws are actuated by external pressure in order to connect the two reinforcement bars end to end, it is not possible to verify and test if the operation has been correctly performed. Trust must then be placed in the operator's skill.
Known devices, as in the technique described in the European patent number 0.098.099, which connect perpendicularly, i.e. radially, to the reinforcement bars by successive passes, act in an unpredictable manner because they don't know exactly whether the bar will be applied in a cross or in a nervure. It is thus necessary to use sleeves of considerable length, on the order of 200 to 250 millimeters, and you cannot ensure that all the connections will be made in a good condition.
The result of the connection actually depends on the pressure applied by the operator and each successive positioning of the tool. Also, too strong a connection may damage the end of the reinforcement bar. In summary, modern devices do not ensure that the modifications of the geometry, and thus the mechanical properties, experienced by the coupler and the bar, are constant during connection, regardless of which reinforcement bar-coupler combination is connected.
Moreover, it is necessary to consider that the reinforcement bars meet the very broad geometric and dimensional standardized tolerances as for their dimensions and rib shapes. Large dimensional variation between different reinforcement bars of the same rated diameter are observed as a result. These differences and dimensional and geometric imperfections also involve variations of the mechanical resistance characteristics for each of the coupler connections on the reinforcement bars.
The known devices are also in most cases manually activated and very slightly mechanized. Because of this, they require a considerable involvement by one or more operators. Many consequences of this absence of automization are harmful with regard to efficiency and productivity of the modem devices.
First of all, the labor cost of performing the connection of couplers on reinforcement bars is very high since it requires the involvement, during the entire operation, of one or more operators. The productivity is often low and the operation of connecting requires considerable time. The wage cost is all the more considerable in that, taking into account the technical particulars and the quality requirement in the performance of the connection of couplers onto the reinforcement bars, the operator must in most cases have suitable training and be sufficiently qualified to perform the connection operations.
Moreover, the known devices use a perpendicular connection with a mobile clamping jaw and a fixed matrix which also leads to a quasi-obligatory misalignment of the two bars to be connected, because the two reinforcement bars are not aligned taking into account the asymmetry and the irregularity of their forms and their dimensions. This misalignment, by turning the traction forces into bending moment and into shear stress, is very detrimental to the mechanical performance of the connections.
Another disadvantage of the modem devices and techniques is that they totally separate the connection phase is itself and the quality control phase of the connections made.
It clearly appears that the assemblies of couplers on reinforcement bars must meet very strict requirements with regard to mechanical resistance, and principally, the resistance to traction. Actually, it is essential for the safety of the constructions that the connections established between the reinforcement bars have very considerable mechanical resistance properties and are, to say the least, as extensive as those of the reinforcement bars themselves.
In order to ensure the quality of the connection, it is necessary to make numerous tests, more often than not of the traction since it is the form of the mechanical stresses which predominates in the use of reinforcement bars. These tests are currently only performed in specialized laboratories.
The traction tests currently performed are particularly costly since they are carried out outside of the production site of the coupler connections onto the reinforcement bars and since they require the additional human involvement of highly qualified personnel.
Moreover, the tests currently performed do not allow periodic or random checks of the different connections. Given the costs of the tests, the necessity of performing them in the laboratory and the time they take, it is currently impossible to check the mechanical characteristics of each of the links made by connection between the couplers and the reinforcement bars. This aspect constitutes a very basic disadvantage of the modem devices since they do not ensure an optimal security of each of the links made by connection given that the traction tests are made in a non-systematic manner.
This disadvantage is all the more harmful since the devices and the techniques of connection currently in use are largely manual. Actually, human involvement makes it so that each connection made has specific and individual characteristics. In fact, it must be recognized that the operator can not repeat all of the connection operations in an absolutely identical manner and that as a result, the mechanical properties of the connections made vary for each coupler reinforcement bar combination.
The traction tests currently performed are often planned in advance. The operator thus knows if the connection that he is going to make will be checked or not. He would then have, of course, the natural tendency to take more care in the connections when the connection is designated for a check. This subjectivity is again detrimental to the overall safety of the connections couplers-reinforcement bars. Thus, the exterior laboratory involves some samples prepared such that there is not, strictly speaking, a security of certainty, taking into account the manipulations which can be performed during the performance of these tests.
As a consequence, the realization of the traction tests, in the laboratory and in a non-systematic manner, does not allow for total certainty as for good mechanical resistance of each of the coupler-reinforcement bar connections.
As a consequence, the devices and the techniques of the modem connection make it difficult to obtain certification in the context of a policy of quality assurance.
Recently, one has seen the development, in numerous industries, of a strategy of quality development in the goal of obtaining an official certification which is the assurance of quality of its activities.
The connection devices of couplers on reinforcement bars currently in use makes such an accreditation difficult. Actually, the accreditation must apply, on the one hand, to the material used for the connection, but also to the quality of the human involvement in performing the connection.
Another disadvantage of the present devices is that they make it difficult to adapt to the deviations and dimensional or geometric imperfections of the reinforcement bars. The tolerances imposed for the manufacture of the reinforcement bars are actually vary large and it is not rare, for example, to notice that a reinforcement bar having an external diameter of 30 millimeters effectively measures 1 or 2 millimeters more or less. Present devices which are less mechanized and do not absolutely use automatic methods do not permit adapting the procedure of the extrusion operation as a function of its dimensional and geometric variations.
In the case where the external diameter of the reinforcement bar is greater than the theoretical diameter, the force imposed on the material of the coupler during crimping is found increased and the plastification of the material is more important.
In the case where the external diameter of the reinforcement bar is less than the theoretical diameter, the force of the crimping will be less important and will lead to modifications of the mechanical properties of the coupler which are totally different from the preceding case. Thus, the present devices do not ensure that during connection, the modifications of the mechanical characteristics to which the coupler is subjected are constant regardless of the assembly reinforcement bar-coupler which is set.
This disadvantage again reinforces the individuality that makes up each coupler-reinforcement bar connection, which is harmful in that it concerns the assurance of the quality of the connection made and greatly puts into perspective the result of the laboratory tests on the samples prepared especially for this purpose.
It thus appears that the present devices which allow the connection of the couplers onto the reinforcement bars unequipped with the reinforcement component do not completely give a satisfactory result. By virtue of these numerous disadvantages, the crimped connection coupler-reinforcement bar is currently a technique of limited diffusion given the interest peculiar to links by connection of couplers onto reinforcement bars.
The purpose of the invention presented here is to compensate for the aforementioned disadvantages and to allow connecting a reinforcement bar whose end does not have any means of connection such as a threading. This lack of threading can be due to corrosion or quite simply to the fact that no mechanical connection has been forecasted in the design. It may also be that this mechanical connection has been cut inadvertently on the construction site.
An advantage of the invention presented here is that it includes particular methods allowing on the one hand, a bending and support of the coupler and on the other hand, connection by displacement of a transfer mold along the axis of the coupler, without transmission of the force to the reinforcement bar.
Another significant advantage of the device presented here is in manufacturing a perfectly regular connection by monitoring that the deformation of the coupler is done in a homogeneous manner over the entire surface, whatever the dimensional tolerance of the reinforcement bar and the shape of its sides.